Open Time is a property of paint that is of high importance to the painter. It is defined as the maximum time paint can be re-worked prior to demonstrating permanently the deformations brought to the paint, such as brush-marks, etc. Water-borne latex paints are known to suffer from a rather short Open Time in comparison to solvent borne paints. The origin of this difference lies in the fact that the binder in water borne paints is not soluble in the continuous phase (water). However, some improvements can be made to extend the Open Time by addition of co-solvents. The demand for lowering VOC (Volatile Organic Compound) in paint requires other solutions for extending Open Time than the addition of co-solvents.
One of the traditional methods to improve Open Time of paint is to add co-solvents, and coalescing agents. The use of glycols or high-boiling solvents is known. However, this is undesirable in paints intended to meet the Volatile Organic Compound limits that are in place today. Another disadvantage of the addition of addition of solvents is the lowering of block resistance, and dirt pick-up can become a problem. EP 1500589 states that an Open Time of 10 min is considered optimal.
EP1500689A1 publication describe the preparation and composition of a water borne coating of an acrylic latex prepared and stabilized with a protective colloid, pigments and extenders, wetting agents or leveling agents, coalescents, and thickener. The coating composition relies upon the presence of PVOH (polyvinyl alcohol) as stabilizer; also, PVOH copolymerized with ethylene (marketed by Kuraray Co. Ltd.) can be used or partial acetylation of the OH groups. Although intended for solvent free paints, EP 1500689 shows the improved Open Time in a gloss paint contains nearly 10% of coalescing agents and co-solvents (nearly 10% PG (propylene glycol) and Texanol® ester alcohol, available from Eastman Chemicals).
U.S. Pat. No. 6,303,189 discloses the addition of a polyurethane (PU) dispersion to an aqueous coating, where Tg (glass transition temperature) of the polyurethane dispersion is less than that of the latex polymer. The PU dispersions have small particle size (30 nm) and a low Tg (˜−50° C.-˜−10° C.). Yet the level of co-solvent (propylene glycol) still was roughly 9.4 wt %.
EP 593,151A1 publication describes an improvement in Open Time by developing a latex having still reactable groups, or mix the latex with compounds that have complementary reactable groups.
WO 02/32980 publication demonstrates the preparation and use of a water dispersible (self) crosslinkable polyurethane, having a relatively low molecular weight. This binder crosslinks by various possible chemical reactions.
EP 62,106A1 publication discloses the manufacturing of acrylate latex and styrene-acrylic latex stabilized with PVOH as protective colloid. Preferably, the latex is stabilized without surfactants.
EP 538,571A1 publication discloses the preparation of latex via a surfactant free emulsion polymerization of a selected mixture of monomers with selected PVOHs. This patent does not mention Open Time as a critical parameter to be improved.
U.S. Pat. No. 4,552,908 discloses an improvement of Open Time in paints by using low molecular weight oligomers that are water dispersible film formers, and having coupling moieties.
U.S. Pat. No. 5,270,380 also discloses the use of a binder that has reactable groups.
U.S. Pat. No. 6,040,368 discloses the preparation and use of a latex with acetoacetate, acetoacetamide, cyanoacetate and cyanoacetamide as pendant groups. Also disclosed is the use of polyether monoamine or diamine having primary amine or secondary amine functionality and an alkylpolyglucoside. These polymers are coupled through reaction of the diamine with the acetoacetate to form enamine structures.
U.S. Pat. No. 6,762,230 discloses a coating with coalescent and a latex polymer, in which the coalescent may be reactable.